1. Field of the Invention
The present invention relates to a continuous crushing method and apparatus, and more particularly to an improved continuous crushing method and apparatus for producing a toner having a low softening point and a small particle diameter, which is preferably used for developing an electrostatic latent image; and a toner having a uniform particle size distribution.
2. Discussion of the Background
Conventionally, a method of producing coarse toner particles having a volume-average particle diameter not greater than 40 μm is so-called a batch method in which a fed amount of a block material to be crushed is same as that of the material crushed. However, the batch method has quite a low productivity because a crushable amount at a time is limited in the batch method. In addition, in order to improve the productivity, an experiment has to be performed to find the crushable amount at a time, i.e., a condition in which the material is not melted by a heat, and it takes time to find an optimum amount.
In the batch method, a toner being crushed is softened by a heat and the following phenomena are observed.
Namely, a toner which is continuously crushed for a long time is melted and has a serious problem in its quality. This problem is avoidable by reducing the fed amount of the material crushed at a time. However, when the fed amount is quickly reduced, the particle sizes of the toner become different with time. Namely, after the crushing is started, in the first half of the long-time continuous crushing, there is a tendency in which a rate of finely powdered toner is large and a rate of coarsely powdered toner is small. To the contrary, it is well known that in the second half of the long-time continuous crushing, a rate of finely powdered toner is small and a rate of coarsely powdered toner is large.
Therefore, the particle size distribution of the toner fed to the next process, i.e., a pulverizing and classifying process, is different with time and such a difference causes a serious quality problem of the toner.
As a matter of course, a continuous crushing method which has by far higher productivity than the batch method is studied, but is not satisfactory yet. In particular, a satisfactory crushing method is not found yet for a toner including an inorganic pigment, which is difficult to pulverize.
Because of these reasons, a need exists for a continuous crushing method and apparatus in which a toner does not melt and deteriorate the quality thereof even when continuously crushed for a long time.